The use of completely digitized communication systems such as the Integrated Service Digital Network (ISDN) is becoming more common. Such systems offer voice data image transmissions to the consumer. By replacing analog voice systems with digital capability, large amounts of information of high quality can be transmitted along copper wires which are used as digital channels.
To carry a digital signal on an analog line, a modem must be used to generate signals of different frequency to represent digital bits. By comparison, a completely digital system does not require a modem. Network interface devices are used to access the system. The standard data rate for an ISDN bearer channel system is 64 kilobits per second (Kbps). Terminal equipment such as a D4 bank or digital private exchange (PBX) can be used to interface a plurality of terminal equipment with a central exchange device. The D4 bank has 24 channel units and can service 24 remote subscribers, each having a transmit line and a receive line which can operate at up to 64 Kbps. The channel units are modular devices which, in general, convert incoming signals to local loop format, respond to test commands and interface to channel bank backplanes.
Digital communication systems supply large amounts of data, voice, and video information at a high signal to noise ratio with a minimum of distortion and efficient interface transfer capability. To assure that such a digital system operates at its optimum characteristic, each communication channel in the system must be fully operational and in the proper state. Conventionally, manual access to the individual channel units for each channel is required to perform functions, such as provisioning, performance reporting, status reporting, alarm reporting. These manual methods are typically awkward, limited in functionality, inefficient and labor intensive.
In a time division multiplexed (TDM) digital communication system, a digital terminal time multiplexes signals received from a plurality of lines into communication channels (or time slots) so that they may be transmitted over a single communications line. At the remote end of the line, the signals are converted in a like digital terminal and distributed on a plurality of channels (or time slots) to remote end users. End users employ Customer Premises Equipment (CPEs) which are coupled to a digital terminal via the aforesaid digital channel units (CUs) to access the system and communicate with the other end users.